g151.g1a2ac88.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at g1a2ac88.usw1.send.mailgun.net.
NS records for this zone are defined at g1a2ac88.usw1.send.mailgun.net.
Question and response
Question
dig g151.g1a2ac88.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
g1a2ac88.usw1.send.mailgun.net. 300 SOA ns-cloud-b1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0